Adjustable mutual coupling



March 30, 1948. TlLLMAN I 2,438,770

ADJUSTABLE MUTUAL COUPLING Filed June 5, 1943 Ihverwtor: John ElTil Imam,

by WW His'Abborney of Fig, 1; and

Patented Mar. 30, 1948 2,438,770 ADJUSTABLE MUTUAL COUPLING John E. Tillman,

General Electric New York Stratford, Conn.,

Company, a corporation of assignor to Application June 5, 1943, Serial No. 489,803 10 Claims. (Cl. 171-777) My invention relates to coupling apparatus for radio receivers and similar communication circuits. It is an object of my invention to provide an improved coupling arrangement for the high frequency transformers used in such circuits.

My invention relates more particularly to powdered iron transformers such as are customarily used in the intermediate frequency stages of a superheterodyne radio receiver. It is another object of my invention to provide an improved means for adjusting the mutual coupling of the windings of such a transformer.

Still another object of my invention is to provide an improved tual coupling may be easily and accurately adjusted over a wide range of values.

One of the features of my invention is the linking of a pair of windings carrying high frequency currents and separated by a common wall having a movable core so that the mutual coupling of the windings may be adjusted by varying the position of this core in the common wall.

A further object of my invention, therefore, is to provide an improved radio frequency transformer in which the reluctance of the common magnetic pathof the transformer windings may be varied easily and accurately by a single adjusting operation.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which Fig. 1 is a side elevation view, partly in section, of a transformer embodying my invention; Fig. 2 is a plan view of the transformer of Fig. 1 along the line 22; Fig. 3 is a side elevation view, partly in section, of a modification of the transformer Fig. 4 is a plan view of the transformer of Fig. 3.

Referring to Fig. 1, I have shown a radio frequency transformer having a main body member Ill. The body member ID, preferably, is formed as a unitary structure by molding or compressing a mass comprising powdered iron particles and then machining as required. The member III has a pair of recesses, or cups, II and ii, these recesses preferably being substantially cylindrical in shape and separated by a common wall l2 through which is bored a centrally located cylindrical hole [2. Two end walls l3, l4 and a base portion I5 complete the structure of the body member ill.

The base member i5 has a pair of shouldered recesses l1, l3 for receiving the lower ends of tubularforms I9, 20, upon which are wound the transformer windings 2!, 22. The forms i9, 20.

transformer in which the mulit radio receiver of preferably are of insulating material of a synthetic resin type, although any other suitable dielectric material may be used. The open ends of the recesses are provided with a closure member 24 having a central opening corresponding to the hole l2 in the body member and the pair of openings through which the tubular forms pass. -The closure member 24 is likewise provided with a plurality of shoulders 20 to fit socurely about the walls [2, l3, l4 forming the sides of the recesses Ii, H'. Apertures 21 are provided in the closure member 24 and leads 30 of the windings may be threaded throughthese apertures for connecting the windings to their associated circuits. A casing 23 of any suitable material, such as a molded phenolic resin, is used to enclose the entire transformer structure. A pair of threaded studs 28 are provided to extend through corresponding holes in the closure member 24, body member I0 and casing 22, to secure the closure member to the body member by means of nuts 39.

Means for adjusting the inductance of the coils indings 2i, 22 to a desired value is provided by the powdered iron cores 3|, 32 adiustably disposed within the forms is and 2!. Embedded in the iron cores, or tuning slugs, 3 I, 32 are threaded members 33 provided with slots 34 at their upper ends so that, by means of these slots N, the position of the cores within the windings of the transformer may be adjusted in a manner to be explained later.

The transformer body It may be supported from a radio chassis 33 by means of the bolts 29. An insulating board 31 is secured to the chassis in any desirable manner. The heads 38 of-the bolts 29 are supported from the chassis 36 and are held in position by means of a nut 39 and the lock washer 4U. Nuts 4|, riveted to mounting board 31 in a well-known manner, provide means for threadedly engaging screws 33 having one of their ends embedded in the tuning cores 3 i, 32 so that, by means of the slots 34, these cores may be raised or lowered within the windings of the transformer, tuning the windings in the usual manner.

In order to provide means to adjust the mutual coupling of the windings 2 I, 22 of the transformer, a core member 44, comprising the circular powdered iron bodies 45, 48 secured in spaced relation to a threaded screw 41, is located in the circular opening l2 in the common wall i2 between the recesses II, The screw 41 is provided with a slot 48 at its upper end and engages a nut 48 soldered to the chassis.

The operation of the transformer described will be discussed with particular reference to its use as an intermediate frequency transformer in a the superheterodyne type. In

Fig. 1, there are shown two dotted paths A and I, Il may.

- flowing through air gap is formed between assayed cores 3i, s2.

spect to their corresponding windings is efiective to vary the self-inductance of the coils 2 l 22 until desired values of inductance for these coils are obtained.

The flux lines 13 are those lines of flux which return t6 the core 3! through the core 32, rather than the walls of the housing, and form a common linkage or coupling of the windings 23, 22. The mutual coupling of the windings 2!, 22, therefore, is determined primarily by the reluctance of the path across the common wall i2 and through the cores Si, 32. If the reluctance of this path is increased, the proportion of the flux lines B in relation to the number of flux lines A is decreased, the number of lines of flux the path A remaining essentially the same. In the transformer of Fig. 1, the reluctance of the path B is controlled by means of the central core member is comprising the powdered iron body members as and it. These members are them. When the core member 84 is in the position shown in Fig. 1, the reluctance of the path B is a minimum. When the body members of core member 55, however, are raised by adjustment of the screw 41 to a position such that the lower edge of member 35 is higher than the upper surface of member 24 and member 65 is at the mid-position of opening I? so'that there is an air gap at the centers of both base member is and closure member 25, the reluctance of the path B is a maximum. In the manufacture of a radio receiver, the position of tuning core id is adjusted by means of the slot 58, as by a screw driver, until the desired mutual coupling is obtained. Since the position of the core H does not afiect, to any substantial amount, the reluctance of the paths for the normal lines of flux A of the windings 2i, 22, the above adjustment of the mutual inductance of the windings 2|, 22 is obtained with substantially no change in the self-inductance of these windings.

After adjustment of the position of the core 44 to secure the desired mutual inductance is determined, the recesses ll, ii, and i2 may be filled with any suitable sealing material, such as wax for holding the transformer winding and the mutual inductance tuning core 44' securely in place. Any further adjustment of the frequency of the transformers is made thereafter by adjustment of the iron cores 3|, 32 with respect to the windings of the transformer to tune these windings to exact resonance with the capacitance of the associated circuits at a desired frequency.

In the construction of the main body 10, the tuning cores Si, 32, 44 and the closure member 24, which also functions as pole pieces for cores 3|, 32, it is preferable to use powdered iron particles having low resistance and high conductance. Better electrostatic shielding is obtained if the particles are uninsulated from each other and are compressed, or otherwise molded, by any suitable method known inthe art.

In the plan view of Fig. 2, is shown the upper in spaced relation so that an surface of the transformer of Fig. 1. This view points out more clearly the relative positions of tuning cores 3i and 32, the mutual inductance adjusting core 35, and the bolts 29 which support the transformer body from the chassis.

In the transformer arrangement shown in Fig. 3, the body member is provided with two reccsses, or cups, 511, 52, end walls 53, as, a center wall 55, and a bottom portion 56. The coil forms 5? and 53, about which are placed the windings 59 and 60, are supported in the recesses Si, 52 in a manner similar to that described in connectlon with the transformer of Fig. l. The recesses 5i and 52 are provided with shoulders 6i and 62 at their upper ends to receive individual closure members 63, 66 of metallic material.

The common wall between recesses 5i and 52 is provided with an opening 66 which extends about two-thirds of the way through this common wall. A variable core 67 for adjusting the mutual coupling of the coils of the transformer is located within the opening 66 and itsposition within that opening may be varied by means of the screw 68 having its 1ower end embedded in the tuning core. A mounting board, similar to the mounting board 31 shown in the arrangement of Fig. 1, may be used in conjunction with the transformer of Fig. 3 for supporting the tuning core 61, by means of screw 68, and the cores 5i and 58, by means of screws 59, iii. The transformer as a whole may be supported from such a mounting board by means of bolts ii.

In this form of my transformer arrangement, adjustment of the position of tuning core Si is effective to introduce a gap in only one side of the mutual inductance path between windings 59, 65 across the common wall 55. This arrangement is especially desirable where a limited amount of space is available for vertical movement of the tuning core M. The principle 0i" operation, however, is essentially the same as that described in conjunction with the transformer arrangement of Fig. l. The essential features of this operation are the establishment of a common wall between windings of a transformer and controlling the reluctance of the mutual fiux path through this common wall. While I have shown this as being done by means of the introduction of an air gap in this path, it is, of course, obvious that introduction of any type of non-magnetic material in this path is effective to control the mutual coupling of the winding- I Fig. 4 is a plan view of the transformer arrangement of Fig. 3, which shows with greater clarity the relative positions of tuning cores 51 and. I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A radio frequency transformer comprising a bodymember of magnetic material having a plurality of recesses therein, each of said recesses having a corresponding winding of said transformer positioned therein, said windings be ing tuned to a desired band of frequencies, a magnetic closure member for said recesses, said recesses being completely encircled by said magnetic material and being separated by a wall of said body member, said wall being included in the common magnetic path of said windings, and means whereby the reluctance of a portion of said wall maybe varied to adjust the coupling between different of said-windings to control the width of said band of frequencies.

2. A radio frequency transformer comprising a body member of magnetic material having a plurality of recesses therein, said recesses being completely encircled by said magnetic material and being separated by a wall of said member, said wall having an air-gap therein, each of said recesses having a corresponding winding of said transformer positioned therein, said windings being tuned to a desired band of frequencies, and magnetic closure members for said recesses, said windings producing flux traversing a path comprising said closure members and'said wall, and the position of said gap in said wall being variable to vary the reluctance of said flux path and the mutual inductance of said windings to control the width of said band of frequencies.

3. A radio frequency transformer comprising a body member or magnetic material having a plurality of recesses therein, each of said recesses being completely encircled by said magnetic material and having a corresponding winding of said transformer positioned therein and tuned to a desired frequency, a magnetic closure member for said recesses, said recesses being separated by a wall of said body member, said wall having an air-gap therein, said gap being included in the common magnetic path of said windings, and a core member located in said gap, said core member being variable in position to vary the coupling between a pair of said windings while maintaining the tuning of said windings.

4. In a radio frequency transformer the combination oi, a magnetic body member, a pair of windings magnetically associated therewith, said windings being completely surrounded by said body memberand being separated by a wall of said body member, said wall being included in the common magnetic path of said windings, and

constant the tuning of 5. A transformer for comprising a magnetic member having a pair radio frequency currents body member, said body of chambers therein separated by awall of said body member, each of said chambers being substantially completely surpair of chambers therein, said chambers being completely surrounded by said body member and being separated by a wall of said member, a winding disposed in each of said chambers tuned to a desired resonance frequency, means for impressing an input voltage across one or said windings to produce flux traversing said wall to provide a desired output voltage across the other 01' said windings over a band of frequencies, means for varying the reluctance of a part of said wall to vary the flux traversing said wall and the width of said band, and means for adjusting the tuning of said windings individually to compensate for changes in the tuning thereof introduced by said variation of reluctance.

7. A radio frequency transformer comprising three parallel legs of magnetic material, a pair of transverse magnetic yokes connecting said legs, a pair of windings encircling respectively the outer two of said legs, means for varying the reluctance of said outer legs to vary the selfinductance of said windings, the other of said legs having an aperture therein, and means to vary the reluctance of the other of said legs to vary the mutual inductance of said windings comprising means for varying the dimensions of said aperture. I

8. A radio frequency transformer comprising three parallel legs of magnetic material, a pair of transverse magnetic yokes connecting said legs, a pair of windings encircling respectively the outer two of said legs, means for varying the position of said outer legs with to vary the self-inductance of said windings, the other of said legs having a gap therein; and means to vary the reluctance of the other of said legs to vary the mutual inductance of said windings comprising means for varying the position of said gap.

The following references are file of this patent:

UNITED STATES PATENTS of record in the Number Name Date 1,683,389 Kaehni Sept. 4, 1928 3. Rose Mar. 10, 1936 2,130,815 Riepka Sept. 20, 1938 respect to said yokes- 

